Geomembrane liners (often called flexible membrane liners) are large sheets of plastic or rubber material used as a barrier to contain liquids in an impoundment. Facilities where these liners are commonly used include hazardous waste impoundments, potable water reservoirs and other surface impoundments.
At certain types of facilities, such as hazardous waste surface impoundments, it is extremely important to know whether the liner is intact and is performing its intended containment function. Failure to detect and repair a leak can lead to serious ground water and surface water contamination.
Geomembrane liners are generally inspected for physical integrity during installation. Such inspection usually consists of a visual inspection of the surface of the individual sheets which are attached to form the liner combined with physical testing of the seams between the various sheets.
A commonly used approach for monitoring the performance of liners after they are put into service has typically been based on ground water sampling using one or more monitoring wells placed at appropriately selected locations around the impoundment. However, this ground water sampling method provides only an indirect indication of leakage and is not timely, since the ground water contamination may not be detected in monitoring wells for some time after a leak in the liner has occurred. By the time a leak has been detected by this method, substantial ground water contamination may have already occurred.
Another source of inadequacy in the ground water sampling method stems from the need to have the monitoring well in the particular aquifer which is transporting the contaminants. An adequate ground water monitoring program, therefore, requires a large number of monitoring wells along the perimeter of the impoundment with a sufficient number of wells sampling water from different levels within the various aquifers under the impoundment. Even the most elaborate ground water monitoring system, however, cannot provide monitoring as accurate and timely as the invention system because of the inherent limitations discussed above.
The method for detecting and locating leaks in geomembrane liner systems uses an electrical measurement technique which takes advantage of the high electrical insulating properties of the liner with respect to the liquid contained above the liner and the soil under the liner. In general, geomembrane liners made from an impervious plastic material or rubber have a very high electrical resistance. A liner installed in a liquid impoundment, therefore, effectively acts as an electrical insulator between the materials contained within the liner and the surrounding environment. If the integrity of the liner is lost due to a puncture or separation, however, conductive liquid may then flow through the leak, thus establishing an electrical path through the liner between the contained liquid and the conductive earth in surrounding contact with the underside of the liner. The low resistance path forms an forms an electrically detectable region corresponding to the location of a leak which may be detected and located.
The electrical measurement technique described above is discussed in greater detail in the publication "Electrical Resistivity Technique to Assess the Integrity of Geomembrane Liners," Final Technical Report, Southwest Research Institute, Project No. 14-6289, EPA Contract No. 68-03-3033 (1984), which by this reference is incorporated for all purposes.